Arrangement for projecting televised images on to a large screen



Oct. 27, 1959 2,910,532

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United States PatentV O ARRANGEMENT FOR PRQJECTING TELEVISED IMAGES N TOA LARGE SCREEN Michel Auphan, Neuilly-sur-Seine, France, assignor toSociete Generale dElectronique, Monaco-Condamine, a societe of MonacoApplication June 14, 1954, Serial No. 436,603 Claims priority,application France June 1S, 1953 6 Claims. (Cl. 17S7.5)

The object of the invention is to provide an arrangement for projectingtelevised images on to a large screen.

This arrangement is of the kind in which the fluorescent screen of thenormal type of cathode-ray tube is replaced by a metallic sheet, thefunction of which is to modulate locally, in association with a suitableoptical system, the light emitted from an external source.

'This metallic sheet or membrane has a refiecting surface and it is ingeneral flat or spherical in the position of rest. It is disposed at avery short distance from an insulating support and, when it is traversedby a pencil of light rays, it charges up the insulating support,especially bysecondary emission. 'Ihe sheet then becomes locallydeformed under the effect of electrostatic forces. The optical systemusually used is of the kind known under the name of the Toepler opticalsystem which transforms this local deformation into a brilliant spot onthe screen. In 'the text which follows, the structure which takes themodulating sheet which has received local deformations proportional Itothe brilliance of each area of the transmitted image, will be known asthe mosaic The principle of a modulating sheet of this kind has beendescribed in the addition of No. P.V. 49,65() of July 19, 1951 to FrenchPatent No. 994,390, applied for on June 9, 1949 in the name of the sameapplicant.

The present invention is more particularly intended to provideimprovements both in the mechanical and in the electrical field, to thesaid modulating sheet and in its conditions of operation.

In the attached drawings:

Fig. l shows a possible form of embodiment of the arrangement forprojecting televised images on to a large screen, utilising an opticalsystem provided with grids.

Figs, 2, 3, 3a, 4 and 5 show different improvements of thelight-modulating system in the case in which the cathode-ray tube is ofthe positive-modulation type.

Fig. 6 shows an arrangement in accordance with the invention which isapplicable to tubes of the negativemodulation type.

Modulation is known as positive for the purposes of the presentdescription, when the maximum intensity of the cathode beam correspondsto the white portions of the image, and is called negative when thismaximum intensity corresponds to the black portion.

Fig. 7 shows a television arrangement on a large screen With an opticalsystem utilising a spherical modulating sheet which forms a concavemirror in its state of rest.

An example of a form of construction of the optical system is given inFig. l, in which T indicates the cathoderay tube and F the modulatingreflecting sheet. In this example, the sheet F is supposed to have aflat surface in the state of rest. A grid, made up of parallel bars G1is suitably illuminated from a source S t lrough a condenser C. Thearrangement of the lens O1 and the sheet F gives an image of this gridG1 in the plane of a second grid G2. The various component members arearranged in such a way that the images of G1 and G2 interlace exactly,that is to say the image of a full bar of the grid G1 is produced e .t1C@ in the space separating two bars of G2 and vice-versa. The result ofthis is that no light passes through G2. If, on the other hand, thesheet is locally deformed, the light is deflected and passes between thebars of G2, thus giving on the projection screen E a brilliant tracecorresponding to the deformed area. It will be noted that the grids G1and G2 may be reduced to two bars: there are then two diaphragms havingthe form of slots. An arrangement of this kind is described in theaddition referred to previously.

Emphasis must be placed on the fact that, in order for the clear partsof the televised image to give a lighted area on the screen, itsorientation must be locally changed when the modulating sheet F isdeformed, this change in orientation being defined by the fact that thenormal moves in a plane which should not be parallel to the bars of thegrid of the Toepler system. When the said plane of movement of thenormal is perpendicular to the bars of the Toepler grid, the modulationis a maximum, since the image of G1 given in the plane of G2 by thesmall portion of surface considered, has been moved at right v angles tothe bars.

If a small portion of the sheet F suffers simply a translation effect,the direction of its normal remains unchanged and the image of theportion considered does not cross the optical system described above.Only the contours of the corresponding area of the screen areilluminated. It follows that the areas of the modulating sheet whichcorrespond to white parts of the screen must assume, under the effect ofthe electronic bombardment, an undulating form, the direction of theseundulations not being prependicular to the direction of the bars of thegrids. The system described in the addition referred to above supposedthat the texture of the television image itself could introduce thisundulation, the density of electronic bombardment being modulated atright angles to the scanning lines. But this modulation is only real ifthe said lines are clearly separate from each other, which is verydifficult to obtain, especially in hiUh-definition Work. It mayfurthermore be observed that, even if the lines are effectivelyseparated, the light contrast depends on the focussing of the tube, andthis is a nuisance.

The methods and arrangements in conformity with the present inventionenable the light-modulating sheet to assume an undulating form in allthe light portions of the televised image, even if the scanning linesare not effectively separated.

(l) In the usual case in which the tube is positively modulated (Figs. 2to 5), the electronic bombardment should cause undulations to appear onthe modulating sheet. As has been explained in the addition referred toabove, the sheet F is generally maintained at a constant distance fromthe insulating support I by a series of parallel strips or spacers whichare called chevrons herein, because of their configuration and which aredenoted by H.

In accordance with the invention, the desired undulation may be obtainedby the various arrangements which follow hereafter, these arrangementsall having a common feature comprising the utilisation of a networkwhich influences the deformation of the sheet:

(a) In the case in which the modulating sheet F is flat, there isarranged, on the side of the electronic bombardment and at a shortdistance from the sheet, a at grid G composed of parallel Wires, inaccordance with the arrangement shown in Fig. 2. The wires cast shadowsduring the electronic bombardment and the sheet is only deformed in theactual areas bombarded, that is to say it assumes an undulated formfollowing the shadow of the wires of the grid. This grid is parallel tothe grids of the optical system considered so as tol obtain maximummodulation, as has been explained above. The insulating supportconstitutes in this case the wall of the tube, and the light arrivesfrom the side of the insulating support following the arrangement shownin Fig. 1. The chevrons which support the sheet are perpendicular to thebars of the grids as to avoid any troublesome diffraction effects.

(b) In accordance with the arrangement shown in Figs. 3 and 3a, thesheet F has alternate thick and thin portions; the bands having the samethickness are at right angles to the chevrons and parallel to the grids.Under the electronic bombardment, the deformation of the sheet varies inaccordance with the thickness of the band in question and this causesthe production of the desired undulations.

(c) In accordance with the arrangement shown in Fig. 4, the sheet F isof uniform thickness but the chevrons are crenellated. The sheet is muchmore free to assume deformation between the tops of each tooth, whichare here known as supporting strips, than along the lines of thesestrips. Under the effect of the electronic bombardment, the sheet alsoassumes an undulating form. It will, of course, be understood that theseteeth should not be visible from the side of the support; the materialwhich constitutes the bottoms of these castellations should thus beopaque.

(d) In a further system (not shown), there is deposited (for example byevaporation under vacuum through a grid), a series of thin bands of abody upon the insulating support. These bands should be suflicientlythin for their optical influence to be negligible, but they should bethick enough for the secondary emission from the support to be modied inthe areas at which it is covered by the strips. The chevrons, must ofcourse, be perpendicular to the strips. By employing a suitable speedfor the incident electrons, there is obtained a secondary emissiongreater than lover the strips and less than 1 between the strips, orvice-versa; the sheet will thus be attracted by the bands and repelledby the spaces between the bands or conversely, and it will thus takeup'an undulating shape. It will also be clear that, quite apart from themethod referred to, in which the strips are obtained by evaporationunder vacuum, any means which enables the application to the support, ofstrips, the secondary emission of which is modied, will fall within thescope of this invention. In accordance with this arrangement, thechevrons are still perpendicular to the grids.

(e) In accordance with an alternative form of the preceding system, theinsulating support is again provided with thin parallel strips of asubstance, but they are no longer provided with the object of modifyinglocally its secondary emission.

The nature of the substance is such that it confers on the insulatingsupport, at the areas covered by the deposit, a certain superficialconductivity. This conductivity should be sulicient for it to be able todischarge the insulating support in a time which is much less than theduration of an image.

It will be understood that, at the moment of the electronic impact, thewhole sheet is also attracted towards the support, but that after a veryshort time, only those portions of the sheet which are not faced bystrips remain attracted, and this accomplishes the desired undulation ofthe sheet during almost the whole ofthe duration of an image.

' (f) The arrangement in accordance with Fig. 5 differs from thepreceding arrangements by the fact that the chevrons which support thesheet -are parallel and not in this case perpendicular torthe grids G1and G2 of the Toepler system, but they are built up in a special Way sothat they do not produce diffraction of the light in the absence ofdeformation of the sheet. In fact, these chevrons are composed of twosubstances 1 and 2, the substance 1 is transparent and the substance 2is preferably metallic, that is to say opaque withpa reflecting surface.The index and the thickness of the substance 1 are so chosen that theoptical thickness of the layer 1 is equal to the distance ofthe movingsheet from the support (the optical length is the product of the reallength multiplied by the index). It follows that the light reiiected bythe chevrons and by` the sheet has the same phase and that the wholearrangement behaves, fromthe optical point of View, as if the chevronsdid not exist. When the sheet is displaced, the phases of the light raysreected by the sheet and by the chevrons are different; the light isdilracted and passes through the grid G2 as in the previous cases.

It is to be noted that, if monochromatic light only is used, thesubstance 1 is no longer useful, provided that the distance between thesheet S and the support I in the state of rest, is equal to a multipleofrhalf a wave-length.

(Z) In the case in which it is preferred to give the modulating sheet anundulating form in the state of rest, the electronic bombardment shouldbe such as to restore the sheet to its plane form. The modulation of thetube must therefore obviously be negative. Y

In accordance with the arrangement shown in Fig. 6, which is given byway of example without limitation, the chevrons may then be undulatingand the sheet may adhere to the entire length of the chevrons; it isthus undulating in its state of rest (or it may have a castellatedshape). The chevrons are perpendicular to the bars of the grids G1 andG2, as in the rst systems described, but the sheet, in its state ofrest, corresponds to the maximum of white. When it is subjected toelectronic bombardment, it adheres to the insulating support and, inconsequence, becomes flat everywhere it is visible, that is to saybetween the chevrons. The areas which are thus stuck together willtherefore correspond to the black part of the image. It is easy to make-up a mosaic of this kind if reference is made to French Patent No. P.V.648,412 of May 19 1953 made in the name of the present applicant. It issufficient to proceed as in the case of the alternative form intended toproduce supporting strips hidden by opaque bands, but to suppress thesecond grid during the evaporation of the substance having a powerfulchemical activity (substance 7); the sheet will then adhere along theentire length of the grooved chevron.

It will be Well understood that in all the systems which have beendescribed above, except the irst, the mosaic does not need to have aplane surface; it may, in particular, be spherical or it may representan optically-defined surface. One application, in accordance with theinvention, of spherical modulating sheets consists in the elimination ofthe lens O1 of the optical equipment. The mosaic, which is then aconcave mirror, gives directly an image of the grid G1 on the grid G2(see Fig. 7).

In all the systems described above, no precise information has beengiven on how the deformations of the sheet were suppressed between eachtelevised image. This result is generally obtained by making theinsulating support slightly conductive. This conductivity must be justenough to permitrthe dissipation through the chevrons (which in thiscase act as conductors) of the charges induced by secondary emission onthe insulating support. This dissipation of the charges must becompleted in a time equal at most to the duration of a television image(that is to say 25th of a second in the case of the standard used inFrance). In order to obtain a support which is slightly conductive,either a material can be used whichris conducting inthe mass, or adeposit may be made (in general by evaporation under vacuum) of aconducting substance on to the insulating support.

The alternative form of embodiment described under (1)(e) is especiallyeasy to carry into effect in the case in which the above-mentioned meansof suppressing `the deformations is employed, since it is much easier toincrease the surface conductivity of a support which'is already aconductor than to make a support which is whollyV Si insulating act as aconductor when, as is the case, the thickness which can be employed forthe conducting strips is limited for optical reasons.

In accordance with a further feature of the invention, the presence ofan electric held in the vicinity of the sheet facilitates itsdeformation under the effect of the electronic bombardment. As far asthe direction of this electric field is concerned, several cases may beconsidered:

(1) If it is desired to charge the support negatively, the electricfield must prevent all secondary electrons from leaving the support andpassing through the moving sheet; in this case, the sheet must becharged to a potential higher than that of the metallisation of thetube.

(2) lf it is desired to charge the insulating support positively, thesecondary electrons must, on the other hand, be attracted far from themosaic. The moving sheet is then charged to a potential less than thatof the metallisation of the tube.

With certain insulating supports, the introduction of such an electricfield is absolutely necessary in 'obtaining a deformation of the sheet`it has even been found that, the' sheet having been deformed, if itspotential is brought back to a value equal to that of the metallisationof the tube, whilst the electronic bombardment is maintained, the sheetresumes its initial state.

In accordance with the present invention, this property may be appliedto a new method of wiping out the mosaic, which avoids the use of aslightly conductive support.

in this method, the mosaic is obliterated during the return of eachline. During these returns, the potential of the sheet is brought hackto a kvalue equal to that of the metallisation of the tube. O n theother hand, the cathode-ray is not cut off during the return-lines butis brought back to a state of constant current; it is, furthermore,slightly deflected towards the base of the image. lt will thus beunderstood that'it will obliterate, in the areas which are to berestored, the line or the few lines which follow.

With this wiping-out system, a positive modulation may be used in thecase of the mosaics described with reference to Fig. 6. In that case, itis during the course of the line itself that the potential of themetallisation is the same as that of the sheet and during thereturn-line, the potential of the rnetallisationl is less than that ofthe sheet, so that during each return-line the sheet re-adheres to thesupport over the bombarded areas.

On the other hand, in order to increase the electric -elds in thevicinity of the mosaic, there may be an advantage in suppressing thespace-charges which could be produced in front of it. In accordance withthe invention, a new improvement in the arrangements suggested consistin placing a grid in front of the mosaic, arranged as shown in Fig. 1.In this case, however, the object sought for is different, and there isno need for the grid to be stretched so close to the mosaic. On theother hand, its wires will then be as line as possible so as tointercept as little as possible of the electron ow. This grid may alsobe replaced by a metallic membrane stretched over a frame, on thecondition that it is line enough not to interfere with the passage ofthe electrons. In both cases, the electric field is applied byestablishing a difference of potential between the moving sheet F andthe grid or the membrane. The grid (or the membrane) does not require tobe very close to the mosaic and can thus be used with a non-planemosaic, for example a spherical mosaic.

What l claim is:

l. In apparatus for the projection of television images utilizing anoptical system and a cathode ray tube, said tube having at least asource of electrons adjacent one end thereof and a modulating elementadjacent the other end thereof, said modulating element including aninsulating support and a thin reflecting metallic sheet held at a shortdistance from said support, means for sweeping said sheet with a beam ofelectrons from said source, said sheet being locally deformable inresponse to the impingement thereon of said beam of electrons, and meansinterfaced between said sheet and said source of electrons to limit theimpingement of said beam to predetermined areas of said sheet.

2. ln a cathode ray tube for the projection of televised images on alarge screen, a modulating element disposed in the position normallyoccupied by the fluorescent screen in conventional tubes, saidmodulating element being locally deformable by an electron beam withinsaid tube and an optical system cooperating therewith for locallymodulating the light emitted by an auxiliary luminous source, thestructure of said modulating element comprising an insulating support, ametallic reflecting sheet held at a short distance from said support,suitable means for supporting said sheet such that normally plane areasbecome rippled and normally rippled areas become plane upon impingernentthereon of said electronic beam.

3. A modulating element as described in claim 2 including holding bandsconnecting said reflecting metallic sheet to said insulating support.

4. A modulating element as defined in claim 2 and incorporated in anoptical system of the Toepler type comprising a grid disposed on theside of said insulating support opposite to said metallic recctingscreen, said grid being parallel to said screen and having its barsparallel to those of the lgrids of said optical system.

5. A structure of a modulating element as dened in claim 2 andincorporated in au optical system of the Toepler type comprising a griddisposed on the opposite side of said metallic reflecting sheet fromsaid insulating support, said grid being parallel to said sheet andhaving its bars parallel to those of said grids of said optical system,and parallel holding bands connecting said sheet to said insulatingsupport and being perpendicular to said bars of said grids.

6. A structure for a modulating element as defined in claim 2 andincorporated in an optical system of the Toepler type comprising a griddisposed on the opposite side of said metallic reflecting sheet fromsaid insulating support, said grid being parallel to said sheet andhaving its bars formed on the metallic sheet itself by thickened areasin the form of parallel bands of equal thickness parallel to the bars ofsaid grids of said optical system.

References Cited in the le of this patent UNITED STATES PATENTS2,510,846 Wikkenhauser June 6, 1950 FOREIGN PATENTS 678,307 GreatBritain Sept. 3, 1952 OTHER REFERENCES Ser. No. 354,771, Paehr et al.(A.P.C.), published May 18, 1943.

